1. Field of the Invention
The present invention relates to a machine for manufacturing a material sheet, in particular a paper or cardboard sheet, with a dryer section including at least one double-row dryer group having two rows of heated dryer cylinders. Each of the two rows of heated cylinders has been assigned a transport belt circulating in a meandering fashion around the dryer cylinders of each row and around the deflection rolls assigned to the respective row of dryer cylinders. The transport belt is adapted to press the material sheet against the surfaces of the dryer cylinders. The machine also includes a drive mechanism, comprising at least one motor associated with each row of dryer cylinders, to rotate the dryer cylinders and deflection rolls and to circulate the transport belts of the dryer section. The drive mechanism is adapted to independently regulate the rotational speeds of the rows of dryer cylinders.
The present invention further relates to a method for manufacturing a material sheet in a dryer section with at least one double-row dryer group having two rows of heated dryer cylinders, each also having a transport belt circulating in a meandering fashion around the dryer cylinders and deflection rolls assigned to the dryer cylinders thereby pressing the material sheet against the surfaces of the dryer cylinders, and a drive mechanism which includes at least one motor assigned to each row of dryer cylinders of the double-row dryer group. The method includes rotating the dryer cylinders and deflection rolls, whereby the transport belts are circulated through the dryer section. The rotational speed of the cylinders in the two rows is driven independently.
2. Discussion of Background Information
Machines of the type generally mentioned herein are discussed, e.g., in DE 33 22 996 C2. This document discloses a dryer section with at least one double-row dryer group. Double-row dryer groups include two rows of heated dryer cylinders, each of which is assigned a felt, also known as a dryer screen, which together with the material sheet circulates in a meandering manner around the dryer cylinders of one row and the deflection rolls assigned to the dryer cylinders, thereby pressing the material sheet against the surface of the dryer cylinders. The material sheet circulates alternatingly around the dryer cylinders of both rows of the double-row dryer group, so that the upper and lower sides of the material sheet alternately come in contact with the dryer cylinders. The known machine exhibits a drive mechanism which sets the dryer cylinders in rotation and causes the felts of the dryer section to circulate.
If a sheet tear occurs, the material sheet is threaded into the machine in the following manner: first, the material sheet is guided only up to the end of a so-called press section or to the beginning of the dryer section and, during a start-up phase, arrives in an area underneath the machine in a discharge-release system. The material sheet runs at nearly full operational speed. Next, a relatively narrow strip, known as a ribbon or threading-strip, is removed from the edge of the sheet. This is then guided through the dryer section, which can consist of single- and double-row dryer groups. It is known that the insertion of the threading strip is problematic. Among other things, ropes have been used to assist in this which, however, do not ensure the required safety in the threading procedure and in addition present a safety hazard to the operating personnel.
It is also known that threading strips can be guided through the machine without the aid of ropes. Scrapers and air jet nozzles, or combined scrapers and air jet nozzles are, for example, used thereby to remove the threading strips from the individual cylinders and guide them through the machine.
It has been determined that errors occur in a great number of cases during such ropeless insertions, so that the threading procedure must be repeated.